They're repeat signs. When you see them at the END of a measure look back in the piece and find the measure that has them at the BEGINNING of it. You repeat the piece from there. In the case of this piece is also has 1st and 2nd endings. So you have to play it as follows: Play from the beginning, when you reach 1st ending, play it through as normal. When you get to the repeat sign, go back to measure 5 and play that section over. When you reach the 1st Ending this time, instead of playing it, jump to the 2nd ending and play that all the way to the end. When you see where it says da capo, jump all the way back to the first measure and do it all over again. When you get to the last measure this time, stop, you're done.